The present invention relates to a process for examining a section of the eye by exposing the section to light by way of a point light source and measuring the backscattered light. The light from the point light source is imaged in a plane, deflected, and directed for scanning the eye section to be examined. The light reflected on the eye section to be examined is sensed and evaluated by optical coherence tomography (OCT technique). The invention further relates to an arrangement for examining a section of the eye having a point light source, an optical imaging device for imaging the point light source in a plane, a scanning device for producing scanning movement of the point light source, and an optical coherence tomography device for evaluating the light reflected by the section of the eye to be examined.
One process and one arrangement of this type are known from U.S. Pat. No. 5,493,109.
For examining the eye, different photography techniques have been used for the anterior and posterior eye sections. In the field of ophthalmology, a fundus camera or a slit lamp has been used, together with an ophthalmoscopy lens such as a contact lens or a Volk lens, for displaying the posterior eye section. The anterior eye section can be displayed by using a slit lamp. Examination of the posterior eye section on the basis of optical coherence tomography (OCT) by way of a fundus camera is known. Corresponding equipment is described, for example, in International Patent Document WO 92/19930 and U.S. Pat. Nos. 5,537,162, 5,506,634, 5,493,109 and 5,321,501. The known equipment is optimized with respect to examination of the posterior section (fundus) of the eye.
An ophthalmologic instrument is known from Japanese Patent Document JP 6-205,741 A, in which a slit lamp is provided as an illuminating system and a measuring device is provided. The measuring device comprises a laser light source, a scanning mirror, a beam splitter, and a photo-electric converter element as well as a light emitter and a filter. The light source emits a directional laser beam for a therapeutic laser light source. Positioning of the directional laser beam is monitored by the photo-electric converter element and the light-emitting element by way of a microscope. When the directional laser has reached a desired position, the therapeutic laser is switched on and the light of this laser is coupled by way of a mirror into the directional laser beam path.
In order to avoid inhomogeneities, particularly of the refracting media, during the OCT of the posterior eye section, a complicated and lengthy adjusting operation is required in order to direct the OCT beam path past the inhomogeneities of the eye to the posterior eye section. When the OCT-technique is used, the adjustment and the targeting operation by which the OCT beam path (sample beam) is directed at the fundus of the eye, particularly at the retina, requires special training and instructions as well as constant practice by the examining physician.
In an arrangement known from FIG. 1 of U.S. Pat. No. 5,537,162, the sample beam path of the OCT interferometer is focussed in the focal plane of a slit lamp microscope. By way of an ophthalmoscopy lens constructed as a Volk lens, in conjunction with the refracting media of the eye, the focal plane of the slip lamp microscope is imaged onto the retina of the eye.
The known arrangement can be used only for OCT-scanning of the posterior eye section. In this case, two separate deviation mirrors are used for producing the sectional views of the eye with an arbitrary alignment. The separate deviation mirrors, however, cause a beam offset and, if the coating is not optimal, produce a double image of the eye. In addition, the working distance between the instrument and the patient's eye is reduced because both deviation mirrors are situated in front of the last optical constructional element of the slit lamp. The use of necessary optical devices, such as an ophthalmoscopy lens, becomes more difficult as a result.